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Comment by onepointsixC | Hacker News Reader

>Supporting the spy angle is the pretty obvious connectivity (looks to be Ku-band satellite or similar) but it also doesn't really make that much sense... surely a satellite does what this does but better? China has no shortage of high quality spy satellites.

Two things. It will be significantly better at ELINT, soaking up signals over which it floats. Second, at 60,000 feet it is at least an order of magnitude closer than LEO spy satellites are, if not more. Simple physics dictates the limits of resolution for the lenses for spy satellites. Being significantly closer makes it much easier to provide better images than a multi billion dollar spy satellite. All at a significantly lower cost.

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This bears repeating. Physics dictates that atmosphere effects means a spy satellite, operating from the edge of space, will never be able to resolve the license plate of a car. A balloon, at 60,000 feet, roughly 18 km (space is at 100 km) can. If you're China, and you want high resolution aerial photography of US nuclear missile silos in Montana, this is what you'd use.

We've been at the limit since the 70's, btw. The Hubble space telescope was enabled by the spy satellite program - they didn't just "happen" to have an extra mirror of exactly the right size, they made them for spy satellites.

https://www.nextbigfuture.com/2019/09/us-spy-satellites-at-d...

If you point the JWT at the earth, can it see moar?

Good question. The answer is no for three primary reasons. First, the JWST isn't designed for observing Earth, so its equipment isn't optimized for that purpose. Second, spy sats are already at the limits of what physics will allow them to see. And third, the JWST is much farther from our planet than spy sats. The atmosphere blurs signals.

That’s true but it assumes it can get within ~40 miles as the crow flies of an interesting target, even then you are going through a LOT more dense atmosphere for your photos.

The satellites still have to take photos through the atmosphere. All of the atmosphere, in fact.

Where an object at 60,000 feet would only have about 95% of the atmosphere below it.

It's an optics problem. Most of the scattering when looking down is near the objects because that's where the turbulence and air density. Looking sideways has to go through all of that - it's dense, uniform, and turbulent in comparison to the atmosphere above a point.

Another way to reframe this is that you would get a higher resolution looking at an object 100 miles down from space then you'd get looking at an equivalent object 100 miles up.

(Keyhole satellites are at 200 miles.)

Of course, knowing when satellites are above you is a bit easier to know and prepare for (the governments usually know where sophisticated adversarial satellites are). The smaller satellites I think are quite a bit higher - 300 miles - so the balloon can probably beat them provided it can get with 100 miles (even though there's a lot of those).

All of politics is an Optics Problem :-)

Funny you mention that because Trump gave away USA-224’s optics capability. You can understand from that photo the kind of resolution you can get from space (during the middle of the day, in August, in a desert - no less).

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